Apparatus for introducing fluid pressure into continuously advancing tubular film



Dee. 2, 1958 K G. GERBER 2 862,234

APPARATUS FOR INIRODUCING FLUID PRESSURE INTO Filed May l8,' 1956 CONTINUOUSLY ADVANCING TUBULAR FILM 2 Sheets-Sheet l l/VVE/VTOR kE/V/VETl-l GEORGEGERBH? ATTORNEYS" Filed May 18, 1956 K G. GERBER ODUCING FLUID PRESSURE INTO CONTINUOUSLY ADVANCING TUBULAR FILM 2 Sheets-Sheet 2 INVENTOR KENNETH GEORGEGERBEE ATTORNEYS United States Patent APPARATUS FOR INTRODUCING FLUID PRESSURE INTO CONTINUOUSLY AD- VANCING TUBULAR FILM Kenneth George Gerber, Welwyn Garden City, England,

assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Application May 18, 1956, Serial No. 585,795

Claims priority, application Great Britain June 3, 1955 5 Claims. (Cl. 18-15) This inventionrelates toimprovements in the manufacture of tubular film of organic thermoplastic materials, and more particularly to apparatus for introducing fluid pressure into a length of continuously advancing tubular film.

At various stages in processes for the production or treatment of tubular film of organic thermoplastic materials fluid pressure is introduced into a section of a continuously advancing length of the film to stretch it or to prevent it from shrinkage, this section being sealed at one or both ends by a pair of nip rolls which forward the tubing and pinch its walls firmly together. Frequently it is necessary to introduce air or other fluid into a section of film between two such pairs of nip rolls, and this has usually been done either by introducing the fluid through an open end of the tubing before this is threaded through the second pair of nip rolls, or by piercing the section to be inflated with a hollow needle, and introducing the fluid therethrough. In both of these methods, however, it is often diflicult to introduce sufficient pressure and to maintain this pressure without significant variation over long periods of continuous operation.

It is an object of the present invention to provide improved apparatus for introducing fluid pressure into a section of a continuously advancing length of tubular film in processes of the type described.

In accordance with the present invention the apparatus -may be used for the continuous production or treatment of tubular film in which a fluid is enclosed within a section of the continuously advancing film, this section being bounded at least at one end by a pair of contra-rotating nip rolls which advance the tubular film and pinch its walls firmly together, and characterised in that said fluid is introduced through a tubular probe passing through the nip of the rolls, at least one of said rolls being circumferentially grooved to provide a passage for the tubular probe, and the tubular probe being held substantially stationary against the rotation of the rolls while the process is in operation.

Our invention further comprises apparatus, for use in the production or treatment of tubular film, that includes a pair of contra-rotatable nip rolls, a tubular probe projecting through the nip thereof, and means for holding said tubular probe stationary against the rotation of the rolls, at least one of said nip rolls having a continuous circumferential groove to provide a passage for said tubular probe through the nip, and said tubular probe being adapted to allow the supply of fluid therethrough.

it is preferred. that both nip rolls be grooved to provide conjointly a passage for the probe, and that each groove be lined with a resilient substance, sponge rubber for example, to reduce the escape of the fluid (usually air) from within the tubular film. This lining may fill the whole of the groove, and even extend beyond the top of the groove, provided that it is sufficiently compressible to allow a passage for the tubular probe when the nip rolls are in their operating position. It is also preferred that the external shape of the transverse section of the tubular probe be substantially elliptical or eye-shaped, and the rolls correspondingly grooved; this facilitates the sealing of the passage against leakage of fluid pressure. If desired, additional tubular probes may be passed through the nip rolls, for example to provide for the withdrawal of fluid and the regulation of the pressure within the film. When two or more probes in all are used, these are preferably placed or joined together side by side or in a group having an approximately elliptical or eye-shaped overall transverse section. They may however be placed apart and the nip rolls suitably grooved at more than one point to receive them. There is normally a slight leakage of air or other inflating medium from the inflated film at this point, but this slight and continuous leakage can very easily be made up through the supply tube and a constant pressure maintained, particularly when a pressure regulating device is used. Moreover, the slight leakage is advantageous in that the escaping fluid provides a cushion between the film and the tubular probe and so facilitates the advancement of the film past the stationary probe.

The apparatus of the present invention may be used, for example: for forming a bubble of air or other fluid in extruded tubing issuing from an extrusion die (as an al- I ternative to supplying the inflating fluid through the core tubing is heat treated to set it in the oriented state; and for inflating the tubing to enable it to be pleated or similarly folded, without creasing, by indenting the inflated film with suitably shaped, externally applied blades, or like a mechanical means, before the tubing is flattened by a pair of nip rolls. The probe or probes may be passed into the interior of the tubular film either through the core of the tube-forming die, or at any point at which the fihn is slit to convert it to flat film, and thence between the paired nip rolls.

Particular embodiments of the apparatus of the present invention are shown diagrammatically in the accompanying drawings, in which:

Figure 1 illustrates a process in which a tubular probe is introduced into a freshly extruded tubular film through the core of the extrusion die and one pair of nip rolls, for the purpose of introducing air to stretch the film transversely and so to orient it; 7

Figure 2 is a section through A--A of Figure 1; and

Figure 3 illustrates a process in which a tubular probe is used to introduce air, to prevent shrinkage, into a section of oriented tubular film which is being heat set as it passes from a first pair of nip rolls to a second pair, after which it is slit at both folds to form two lengths of fiat film.

In Figure 1, 1 represents the tube-forming die through which the tubular film, 2, is extruded. The film is .immedi ately chilled by suitable cooling means (not shown) and is then flattened by a first pair of nip rolls, 3. A tubular probe, 4, passes through the hollow core of the extrusion die and through the nip rolls, 3, for the purpose of introducing air into the tubular film and maintaining therein a desired constant pressure that is greater than the pressure surrounding the outside of the tubing; the air so introduced is held'within a limited section of the film by means of the second pair of nip rolls, 5. The tubular probe is fixed to maintain its position against the movement of the rolls. After passing between the first nip rolls, 3, the film is warmed to a suitable drawing temperature by radiant or other heating means (not shown) and'tlie pressure inside the film is adjusted to give the desired increase in width on drawing. Forward drawing may simultaneously be accomplished by driving the nip rolls, 5, at a peripheral speed greater than that of the nip rolls, 3.

The tubular probe, 4, includes an air supply tube and a static. pressure line through which the pressure may be regulated to hold the drawn film constantly to the desired diameter. The construction of the probe at the section held in the nip of the rolls is shown in Figure 2, in which: 3 is one of the pair of nip rolls, each of which has a central circumferential groove, 6, lined with a layer of sponge rubber, 7; 2 is the flattened film as it passes through the nip; 8 is the air supply tube of the probe and 9 the static pressure line, these two tubes being in this instance united at least in the nip region by the solid casing, 10. This casing is so shaped that the probe fits snugly into the grooves of the rolls, and allows only a slight escape of air pressure from beyond the rolls.

In Figure 3, 2 represents the film which is being held in a fully inflated condition between the two pairs of nip rolls, 11 and 12, while radiant or other heaters (not shown) are provided to heat the film to the setting temperature. The fixed tubular probe, 4, which is constructed as shown in Figure 2, passes through the nip rolls 12, which are identical in construction with the nip rolls 3 in Figure 2, and through it pressure is supplied to and regulated within the tubular film between the nip rolls to prevent or control any change in diameter of the film during heat setting. After leaving the nip rolls 12 the tubular film is slit along each fold and the two resulting lengths of flat film are separately wound at 13 and 14.

In some instances, particularly when two or more regions of the film need to be separately inflated for different steps in one continuous process for the production or treatment of tubular film, it may be necessary to pass the tubular probe through two or more pairs of nip rolls before reaching the region of the film that is to be inflated. This can readily be done in accordance with the invention, particularly if the axis of the inflating bubble to be formed is substantially in line with the direction of one of the possible entries for the air tube into the film: that is, with the extrusion orifice or with any point at which the film is longitudinally slit. For example, when a length of film is to be cold drawn, and then heat set at two adjacent inflation areas sealed by a series of three pairs of nip rolls, and slit on emergence from the last pair of nip rolls, two probes or two pairs of probes may be passed through the last pair of rolls into the heat setting area, and one probe or pair of probes may be carried on through the next pair of nip rolls into the cold drawing area. The required air pressure in each inflation area may thus be introduced and regulated. Similarly, a probe or pair of probes entering the tubular film through the core of the extrusion die may be passed through more than one pair of nip rolls to reach the required inflation area.

"for-supplying an inflating medium to a'regionofthe tubular film that must be closed at both ends by nip rolls, it can be used in cases where only one end of the region is closed in this way. For example, where a tubular film is being extruded in the molten state, stretched immediately by enclosed air, collapsed by nip rolls and slit longitudinally along one or more lines, the inflating air may be introduced through the nip rolls, by the use of the apparatus of this invention, instead of through the core of the extrusion die in the customary manner.

The apparatus of the present invention may be used in the production of film from any organic thermoplastic material that can be extruded to give film in tubular form. Such materials include, for example: polythene; linear film-forming superpolyesters such as polyethylene terephthalate; linear superpolyamides; certain vinyl polymers and copolymers such as polyvinyl chloride, polystyrene, polyvinylidene chloride and vinyl chloride/vinylidene chloride copolymers; and cellulose derivatives such as cellulose acetate.

I claim:

1. Apparatus for the continuous treatment of tubular film including means for confining a body of fluid Within a section of the continuously advancing film, said means comprising a pair of contra-rotating, substantially cylindrical nip rolls, at least one of said nip rolls having a relatively small circumferential groove therein, and a tubular probe extending between said nip rolls, said groove fitting closely about said probe.

2. Apparatus as defined in claim 1, wherein said probe is substantiallyelliptical in cross-section.

3. Apparatus as defined in'clairn 1, including a resilient lining in each of said grooves.

4. Apparatus for the continuous production and treatment of tubular film including a tube forming die and means for confining a body of fluid within a section of the continuously advancing film, said means comprising a pair of contra-rotating, substantially cylindrical nip rolls, each of said nip rolls having a relatively small circumferential groove therein, and a tubular probe extending through said tube forming die and between said nip rolls, said grooves enclosing and fitting closely about said probe.

5. Apparatus as defined in claim 1, in which each of said nip rolls has a relatively small circumferential groove therein, the two grooves together enclosing and fitting closely about said probe.

Reterences Cited in the file of this patent UNITED STATES PATENTS 1,612,509 Henderson et al Dec. 28, 1926 2,541,064 Irons Feb. 13, 1951 2,763,029 Tulloss Sept. 18, 1956 

